Mechanisms for forming bonding structures

ABSTRACT

Embodiments of mechanisms for forming a package are provided. The package includes a substrate and a contact pad formed on the substrate. The package also includes a conductive pillar bonded to the contact pad through solder formed between the conductive pillar and the contact pad. The solder is in direct contact with the conductive pillar.

This application is a divisional application of U.S. patent applicationSer. No. 13/944,334, filed Jul. 17, 2013, entitled Mechanisms forForming Bonding Structures,” which application is hereby incorporatedherein in its entirety.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, or otherelectronic equipment. The semiconductor devices are fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductor layers over a semiconductor substrate, andpatterning the various material layers using lithography and etchingprocesses to form circuit components and elements on the semiconductorsubstrate.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. These smallerelectronic components also require a smaller package that utilizes lessarea or a smaller height, in some applications.

New packaging technologies, such as package on package (PoP), have begunto be developed, in which a top package with a device die is bonded to abottom package, with another device die. By adopting the new packagingtechnologies, the integration levels of the packages may be increased.These relatively new types of packaging technologies for semiconductordevices face manufacturing challenges.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompany drawings, in which:

FIG. 1 shows a perspective view of a package structure, in accordancewith some embodiments.

FIGS. 2A and 2B are cross-sectional views of two packages before andafter they are bonded to form a package structure, in accordance withsome embodiments.

FIG. 2C is a cross-sectional view of two packages before they arebonded, in accordance with some embodiments.

FIGS. 3A and 3B are perspective views of stages of a process forarranging conductive pillars in a support substrate, in accordance withsome embodiments.

FIGS. 3C-3E are cross-sectional views of various stages of a process forforming a package, in accordance with some embodiments.

FIGS. 4A-4E are cross-sectional views of portions of packages, inaccordance with some embodiments.

FIGS. 5A-5C are cross-sectional views of portions of packages, inaccordance with some embodiments.

FIGS. 6A-6D are cross-sectional views of portions of package structures,in accordance with some embodiments.

FIG. 7 is a cross-sectional view of a package, in accordance with someembodiments.

FIG. 8 is a cross-sectional view of a package structure, in accordancewith some embodiments.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentscan be embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative, and do not limit thescope of the disclosure.

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the performance of a first process before a second process in thedescription that follows may include embodiments in which the secondprocess is performed immediately after the first process, and may alsoinclude embodiments in which additional processes may be performedbetween the first and second processes. Various features may bearbitrarily drawn in different scales for the sake of simplicity andclarity. Furthermore, the formation of a first feature over or on asecond feature in the description that follows include embodiments inwhich the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedbetween the first and second features, such that the first and secondfeatures may not be in direct contact.

Some variations of the embodiments are described. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements.

FIG. 1 shows a perspective view of a package structure 100 having apackage 110 bonded to another package 120, which is further bonded to asubstrate 130, in accordance with some embodiments. Package 110 isbonded to package 120 via bonding structures 115, and package 120 isbonded to substrate 130 via bonding structures 125. Each package, suchas package 110 or package 120, includes one or more semiconductor dies.The semiconductor die includes a semiconductor substrate as used insemiconductor integrated circuit fabrication, and integrated circuitsmay be formed in and/or on the semiconductor substrate. Thesemiconductor substrate is defined to mean any construction includingsemiconductor materials, such as a bulk silicon, a semiconductor wafer,a silicon-on-insulator (SOI) substrate, or a silicon germaniumsubstrate. Other semiconductor materials including group III, group IV,and group V elements may also be used.

The semiconductor substrate may further include isolation features (notshown), such as shallow trench isolation (STI) features or localoxidation of silicon (LOCOS) features. The isolation features may defineand isolate various device elements. Examples of the various deviceelements that may be formed in the semiconductor substrate includetransistors (e.g., metal oxide semiconductor field effect transistors(MOSFET), complementary metal oxide semiconductor (CMOS) transistors,bipolar junction transistors (BJT), high voltage transistors, highfrequency transistors, p-channel and/or n-channel field effecttransistors (PFETs/NFETs), etc.), diodes, or other suitable elements.Various processes are performed to form the various device elementsincluding deposition, etching, implantation, photolithography,annealing, and/or other suitable processes. The device elements areinterconnected to form the integrated circuit device, such as a logicdevice, memory device (e.g., SRAM), RF device, input/output (I/O)device, system-on-chip (SoC) device, combinations thereof, and otherapplicable types of devices.

Substrate 130 may be a semiconductor wafer, or a portion of a wafer. Insome embodiments, substrate 130 includes silicon, gallium arsenide,silicon on insulator (“SOI”), or other similar materials. In someembodiments, substrate 130 also includes passive devices such asresistors, capacitors, inductors, and the like, or active devices suchas transistors. In some embodiments, substrate 130 includes additionalintegrated circuits. Substrate 130 may further include through substratevias (TSVs) and may be an interposer. In addition, substrate 130 may bemade of other materials. In some embodiments, substrate 130 is a packagesubstrate, such as a multiple-layer circuit board. In some embodiments,the package substrate also includes bismaleimide triazine (BT) resin,FR-4 (a composite material composed of woven fiberglass cloth with anepoxy resin binder that is flame resistant), ceramic, glass, plastic,tape, film, or other supporting materials that may carry conductive padsor lands needed to receive conductive terminals.

In some embodiments, each bonding structure 115 between packages 110 and120 is formed by using a ball-to-ball bonding process. Two solder ballsformed on opposite packages 110 and 120 are reflowed together to formone bonding structure 115. Similarly, bonding structures 125 betweenpackage 120 and substrate 130 may be formed by using the ball-to-ballbonding process described above.

Due to CTE (coefficient of thermal expansion) mismatch between packages110 and 120, warpage of packages 110 and 120 may occur during a reflowprocess. To ensure that the solder balls on opposite packages 110 and120 contact with each other to form bonding structures 115, large solderballs are used. As a result, spaces between adjacent bonding structures115 are reduced, and the bridging risk is increased. In addition, duringthe ball-to-ball bonding process, the solder balls may slide and/orshift, which also leads to high bridging risk between bonding structures115. Bonding structures 125 between package 120 and substrate 130 mayalso suffer from similar high bridging risk.

Bonding structures, such as bonding structures 115 or 125, may usethrough molding vias (TMVs) surrounded by a molding compound to reducethe bridging risk. However, the formation of TMVs involves formingopenings in the molding compound by using a laser drilling process.Fabrication cost and time will increase with the number of TMVs. Inaddition, the pitch between bonding structures involving TMVs is highdue to limitation imposed by the laser drilling process.

Therefore, it is desirable to find alternative mechanisms for formingbonding structures 115 or 125. FIGS. 2A and 2B are cross-sectional viewsof two packages before and after they are bonded to form a packagestructure 200, in accordance with some embodiments.

As shown in FIG. 2A, packages 110 and 120 are provided and ready forbonding, in accordance with some embodiments. In some embodiments,package 110 includes two semiconductor dies 224 and 226, andsemiconductor die 224 is disposed over semiconductor die 226. However,package 110 could include a single semiconductor die or more than twosemiconductor dies. In some embodiments, there is a glue layer (notshown) between semiconductor dies 224 and 226. Semiconductor dies 224and 226 may include various device elements, such as memory devices.

Semiconductor die 226 is bonded to a substrate 216. Substrate 216 may bea semiconductor substrate including the various materials and/orcomponents described above. Alternatively, substrate 216 may be apackage substrate including the various materials described above.Semiconductor die 224 is electrically connected to conductive elements(not shown) formed on or in substrate 216 via bonding wires 228, inaccordance with some embodiments. Similarly, semiconductor die 226 iselectrically connected to the conductive elements formed on or insubstrate 216 via bonding wires 230. Alternatively, semiconductor dies224 and 226 are electrically connected to the conductive elements formedon or in substrate 216 via through substrate vias (TSVs) formed insemiconductor dies 224 and 226. Package 110 also includes a moldingcompound 232, which covers semiconductor dies 224 and 226 and bondingwires 228 and 230.

As shown in FIG. 2A, package 110 includes a passivation layer 220 formedon a bottom surface of substrate 216. Passivation layer 220 may includea solder resist layer, PBO layer, polyimide layer, epoxy layer, or otherapplicable dielectric layers. Passivation layer 220 has openings whichexpose contact pads 218 formed over the bottom surface of substrate 216.Contact pads 218 may be electrically connected to interconnectstructures in substrate 216, and the interconnect structures may befurther connected to devices in semiconductor dies 224 and 226 throughbonding wires 228 and 230. In some embodiments, passivation layer 220 isnot needed. Package 110 also includes a number of solder bumps 221formed on contact pads 218 which are exposed.

As shown in FIG. 2A, package 120 includes a semiconductor die 208 bondedto a substrate 202. Connectors 210 are formed between semiconductor die208 and substrate 202 to electrically connect semiconductor die 208 withconductive elements (not shown) formed on or in substrate 202. Substrate202 may be a semiconductor substrate including the various materialsand/or components described above. Alternatively, substrate 202 may be apackage substrate including the various materials described above.

As shown in FIG. 2A, a number of contact pads 206 are formed on an uppersurface of substrate 202. A passivation layer 204 is deposited andpatterned over substrate 202. Passivation layer 204 has openings whichexpose portions of contact pads 206. Contact pads 206 may electricallyconnect to interconnect structures in substrate 202 and passivationlayer 204 and therefore in communicate with semiconductor die 208through connectors 210. In some embodiments, a number of conductiveconnectors 201 are formed on a bottom surface of substrate 202.Conductive connectors 201 are used to electrically connect to otherconductive elements formed on another substrate, such as substrate 130shown in FIG. 1. Therefore, conductive pads 206 may electrically connectto the interconnect structures in substrate 202 and in communicate withanother substrate through conductive connectors 201. In someembodiments, passivation layer 204 is not needed.

As shown in FIG. 2A, a number of conductive pillars 214 are attached tocontact pads 206 through solder 212, in accordance with someembodiments. In some embodiments, conductive pillars 214 are placed onsolder 212 applied on contact pads 206. Afterwards, a reflow process isperformed to bond conductive pillar 214 on contact pads 206 by solder212 between conductive pillar 214 and contact pads 206. Conductivepillars 214 are secured on contact pads 206 after the reflow process. Asshown in FIG. 2A, package 110 is positioned above and aligned withpackage 120 such that solder bumps 221 are aligned with conductivepillars 214.

In some embodiments, conductive pillars 214 are made of Cu, Al, Cualloy, Al alloy, Au, other applicable materials, or combinationsthereof. In some embodiments, each conductive pillar 214 has a height ina range from about 100 μm to about 300 μm. In some embodiments, eachconductive pillar 214 has a diameter in a range from about 50 μm toabout 200 μm.

As shown in FIG. 2B, packages 110 and 120 are bonded through bondingstructures 215 to form package structure 200, in accordance with someembodiments. Package 110 is placed over package 120 and pressed topackage 120 during a second reflow process. During the second reflowprocess, solder bumps 221 are reflowed to correspondingly coverconductive pillars 214, and therefore forming bonding structures 215.Each bonding structure 215 includes contact pad 218, a solder element242, conductive pillar 214, and contact pad 206. Solder element 242 isformed by reflowing solder 212 and solder bump 221 shown in FIG. 2A.

As shown in FIG. 2B, conductive pillars 214 surrounded by solder element242 are tall and slender, and therefore pitch P between bondingstructures 215 (e.g. between conductive pillars 214) is reduced. In someembodiments, pitch P is in a range from about 150 μm to about 500 μm. Inaddition, such bonding processes reduce the sliding and shiftingproblems.

Alternatively, conductive pillars 214′ may be attached to package 110.FIG. 2C is a cross-sectional view of two packages before they arebonded, in accordance with some embodiments. Conductive pillars are notlimited to be formed on the bottom package (package 120). As shown inFIG. 2C, conductive pillars 214′ are attached to contact pads 218 ofpackage 110 through solder 212′. Package 110 is positioned above andaligned with package 120. Conductive pillars 214′ are aligned withsolder bumps 221′ formed on contact pads 206 of package 120. After thealignment is performed, a process similar to that described in FIG. 2Bmay be performed to form a package structure similar to packagestructure 200 shown in FIG. 2B.

Packages having conductive pillars may be formed by using a variety ofprocesses. FIGS. 3A and 3B are perspective views of stages of a processfor arranging conductive pillars 214 in a support substrate 302, inaccordance with some embodiments. FIGS. 3C-3E are cross-sectional viewsof various stages of a process for forming package 120, in accordancewith some embodiments.

As shown in FIG. 3A, a number of conductive pillars 214 are spread outon support substrate 302 having multiple cavities 304, in accordancewith some embodiments. In some embodiments, conductive pillars 214 havesubstantially planar top surfaces. In some other embodiments, conductivepillars 214 have curved top surfaces. Conductive pillars 214 may beformed by cutting a conductive wire, such as a Cu wire. Supportsubstrate 302 may be made of bakelite, plastic steel, metal, or otherapplicable materials. Each cavity 304 of support substrate 302 has adiameter similar to or slightly larger than that of each conductivepillar 214. Cavities 304 may be formed by using a laser drillingprocess, mechanical drilling process, etching process, or otherapplicable processes. The number of conductive pillars 214 is largerthan or equal to the number of cavities 304.

In some embodiments, support substrate 302 is vibrated by using anagitation generator (not shown) such that conductive pillars 214 fallinto cavities 304, respectively. After each cavity 304 contains oneconductive pillar 214, excess conductive pillars 214 outside of cavities304 are removed, as shown in FIG. 3B. In some embodiments, eachconductive pillar 214 is lodged in one of cavities 304. In someembodiments, a vacuum system (not shown in FIG. 3B) is attached to thebackside of support substrate 302 to keep conductive pillars 214 stay incavities 304. In some embodiments, the vacuum system is turned on whensupport substrate 302 is vibrated to allow conductive pillars 214falling into cavities 304.

In some embodiments, conductive pillars 214 are made of Cu, and aprotection layer is coated on conductive pillars 214. For example, theprotection layer is coated on conductive pillars 214 after eachconductive pillar 214 is located in one cavity 304. In some otherembodiments, the protection layer is coated on conductive pillars 214before they are spread out on support substrate 302. The protectionlayer may include an Ni layer, Ag layer, Ti layer, another applicablelayer, or combinations thereof. The protection layer may preventconductive pillars 214 from being oxidized.

As shown in FIG. 3C, support substrate 302 has holes 306 connected withcavities 304, in accordance with some embodiments. In some embodiments,holes 306 are connected with a vacuum chamber 308, and vacuum chamber308 is further connected to a vacuum system 312. Vacuum system 312 isused to secure conductive pillars 214 through holes 306. However, insome other embodiments, holes 306, vacuum chamber 308, and vacuum system312 are not required. As shown in FIG. 3C, support substrate 302 ispositioned over substrate 202, such that conductive pillars 214 arealigned with solder 212 applied over conductive pads 206.

As shown in FIG. 3D, after the alignment is performed, conductivepillars 214 are placed on solder 212 on contact pads 206, in accordancewith some embodiments. Afterwards, vacuum system 312 is turned off.After vacuum system 312 is turned off, a reflow process 310 is performedto reflow solder 212 such that conductive pillars 214 are bonded tocontact pads 206. Support substrate 302 is used to hold conductivepillars 214 during reflow process 310.

Each conductive pillar 214 has a width W_(c), and each contact pad 206has a width W_(p). In some embodiments, a ratio of width W_(c) to widthW_(p) is smaller than ½, such as in a range of about 0.2 to about 0.49.Support substrate 302 is used to hold conductive pillars 214 duringreflow process 310. Support substrate 302 prevents conductive pillars214 from collapsing during reflow process 310.

In some embodiments, the ratio of width W_(c) to width W_(p) is largerthan ½, such as in a range of about 0.51 to about 1.2. Since width W_(c)is relatively large, each conductive pillar 214 may not easily collapseduring reflow process 310. Therefore, support substrate 302 is notneeded to hold conductive pillars 214 during reflow process 310.However, in some embodiments, support substrate 302 is still used tohold conductive pillars 214 during reflow process 310 even if the ratioof width W_(c) to width W_(p) is larger than ½.

After reflow process 310, support substrate 302 is removed, and package120 is formed, as shown in FIG. 3E. Package 120 includes conductivepillars 214 bonded to contact pads 206 through solder 212 betweenconductive pillars 214 and contact pads 206. In some embodiments, solder212 is in direct contact with one of conductive pillars 214 and one ofcontact pads 206, while conductive pillars 214 are not in direct contactwith contact pads 206. After package 120 is formed, package structure120 is bonded to package 110 through bonding structures 215, as shown inFIGS. 2A-2B.

Package 120 having conductive pillars 214 has many variations. FIGS.4A-4E are cross-sectional views of portions of packages 120, inaccordance with some embodiments.

In some embodiments, conductive pillar 214 has a single width, and theratio of width of conductive pillar 214 to width of contact pad 206 isvariable. As shown in FIG. 4A, a ratio of a width W_(ca) of a conductivepillar 214 a to width W_(p) of contact pad 206 is smaller than ½, inaccordance with some embodiments. The ratio of width W_(ca) ofconductive pillar 214 a to width W_(p) of contact pad 206 may be in arange from about 0.2 to about 0.49. As shown in FIG. 4B, a ratio of awidth W_(cb) of a conductive pillar 214 b to width W_(p) is larger than½ but smaller than 1, in accordance with some embodiments. The ratio ofwidth W_(cb) of conductive pillar 214 b to width W_(p) of contact pad206 may be in a range from about 0.51 to about 0.9. As shown in FIG. 4C,a ratio of width W_(cc) of a conductive pillar 214 c to width W_(p) islarger than 1, in accordance with some embodiments. The ratio of widthW_(cc) of conductive pillar 214 c to width W_(p) of contact pad 206 maybe in a range from about 1.1 to about 1.5.

In some other embodiments, conductive pillar 214 has a narrow topportion and a wide bottom portion. The top portion has a width largerthan that of the bottom portion. In various embodiments, a ratio of thewidth of the wide bottom portion to width W_(p) of contact pad 206 isvariable.

As shown in FIG. 4D, a conductive pillar 214 d has two different widthsW_(wd) and W_(nd). Width W_(wd) of bottom portion 315 b of conductivepillar 214 d is smaller than width W_(p) of contact pad 206, inaccordance with some embodiments. A ratio of width W_(wd) to width W_(p)is larger than ½, such that bottom portion 315 b of conductive pillar214 d may function as a support base of conductive pillar 214 d. Theratio of width W_(wd) of bottom portion 315 b of conductive pillar 214 dto width W_(p) of contact pad 206 may be in a range from about 0.51 toabout 0.9. The ratio of width W_(nd) to width W_(p) may be in a rangefrom about 0.1 to about 0.4.

As shown in FIG. 4E, width W_(we) of bottom portion 315 b of aconductive pillar 214 e is larger than width W_(p) of contact pad 206,in accordance with some embodiments. The ratio of width W_(we) of bottomportion 315 b of conductive pillar 214 e to width W_(p) of contact pad206 may be in a range from about 1.1 to about 1.5. The ratio of widthW_(ne) to width W_(p) may be in a range from about 0.1 to about 1.

Embodiments of the disclosure have many variations. For example, theamount of solder 212 is variable. FIG. 5A shows a structure similar tothat shown in FIG. 4A except solder 212 having a larger amount (volume)than that shown in FIG. 4A. In some embodiments, solder 212 covers acenter point C of the sidewall surface of conductive pillar 214 a. Asshown in FIG. 5A, the top of solder 212 is higher than center point C.

FIG. 5B shows a structure similar to that shown in FIG. 4B except solder212 having a larger amount (volume) than that shown in FIG. 4B. As shownin FIG. 5B, a larger amount (volume) of solder 212 is used, and solder212 covers center point C of the sidewall surface of conductive pillar214 b. As shown in FIG. 5B, the top of solder 212 is higher than centerpoint C.

FIG. 5C shows a structure similar to that shown in FIG. 4D except solder212 having a larger amount (volume) than that shown in FIG. 4D. As shownin FIG. 5C, solder 212 covers a center point C′ of a sidewall surface ofupper portion 315 a of conductive pillar 214 d. As shown in FIG. 5C, thetop of solder 212 is higher than center point C′.

As mentioned above, package 120 having conductive pillars 214 has manyvariations. In addition, package structure 200 having bonding structure215 including conductive pillars 214 also has many variations. FIGS.6A-6D are cross-sectional views of portions of package structures 200,in accordance with some embodiments.

In some embodiments, package 120 shown in FIG. 4A is bonded to package110 (see FIG. 2A) to form package structure 200, as shown in FIG. 6A.Solder 212 and solder ball 221 are reflowed together to form solderelement 242, and bonding structure 215 is formed. In some embodiments,solder element 242 covers sidewall surfaces of conductive pillar 214 a.In some embodiments, solder element 242 covers the entire surface ofconductive pillar 214 a.

As shown in FIG. 6A, since solder 212 and solder ball 221 are reflowedand elongated to form solder element 242, the stress in solder element242 is redistributed. If packages 110 and 120 are bonded by a roundsolder bump having a ball shape, high stress may concentrate at cornerregions of the bonding structure, resulting in bump cracking and reducethe yield of package structure. However, the stress in elongated solderelement 242 is redistributed, and therefore the corner regions ofelongated solder element 242 suffer from less stress than the regularround solder bump.

It is noted that although a width of solder element 242 at a centralportion of conductive pillar 214 a is smaller than that at end portionsof conductive pillar 214 a, solder element 242 may be in other shapes.For example, the width of solder element 242 at the central portion ofconductive pillar 214 a may be the same with or slightly larger thanthat at the end portions of conductive pillar 214 a.

Instead of conductive pillar 214 a, conductive pillar 214 b in FIG. 4Bmay be used to be bonded to package 110, and solder element 242 may alsocover sidewall surfaces of conductive pillar 214 b (not shown).

In some embodiments, package 120 shown in FIG. 4C is bonded to package110 (see FIG. 2A) to form package structure 200, as shown in FIG. 6B.Conductive pillar 214 c is pressed to solder bump 221 and the secondreflow process is performed. After the second reflow process, solderbump 221 is reflowed to form solder 222 by which conductive pillar 214and contact pad 218 are bonded, and bonding structure 215 is formed. Insome embodiments, the sidewall surface of conductive pillar 214 c is notcovered by any solder.

In some embodiments, package 120 shown in FIG. 4D is bonded to package110 (see FIG. 2A) to form package structure 200, as shown in FIG. 6C.Solder 212 and solder bump 221 are reflowed together to form solderelement 242. A bonding structure 215′ is therefore formed. Bondingstructure 215′ includes contact pad 218, solder element 242, conductivepillar 214 d, and contact pad 206. In some embodiments, solder element242 covers sidewall surfaces of conductive pillar 214 d. In someembodiments, solder element 242 covers the entire surface of conductivepillar 214 d.

In some embodiments, package 120 shown in FIG. 4E is bonded to package110 (see FIG. 2A) to form package structure 200, as shown in FIG. 6D.Conductive pillar 214 e is pressed into solder bump 221 during thesecond reflow process is performed. After the second reflow process,solder bump 221 is reflowed to form solder 222 by which conductivepillar 214 e and contact pad 218 are bonded. Bonding structure 215′ istherefore formed.

In some embodiments, various conductive pillars are used in package 120.FIG. 7 is a cross-sectional view of package 120 having two or moredifferent shapes of conductive pillars, such as conductive pillars 214 aand 214 d, in accordance with some embodiments. As shown in FIG. 7,conductive pillar 214 a has a single width W_(c), and conductive pillar214 d has two different widths W_(n) and W_(w). Conductive pillars 214 aand 214 d are both bonded to contact pads 206 by solder 212. In someembodiments, a support substrate (not shown), having both large cavitiesand small cavities, is used to secure conductive pillars 214 a and 214d. In some embodiments, conductive pillars 214 a are first secured inthe large cavities in the support substrate, and conductive pillars 214d are secured in the small cavities in the support substrate afterwards.Processes similar to the embodiments described in FIGS. 3A-3E areperformed, and package 120 having both conductive pillars 214 a and 214d are formed.

In some embodiments, the melting point of solder bump 221 of package 110is higher than the melting point of solder 212. Therefore, when thesecond reflow process is performed to bond conductive pillar 214 withcontact pad 218, solder 212 may melt before solder bump 221 does. As aresult, conductive pillar 214 collapses during the second reflowprocess, and yield of package structure 200 is reduced.

In order to reduce or resolve the problem mentioned above, a protectivelayer 702 is formed to prevent conductive pillars 214 from collapsing.FIG. 8 is a cross-sectional view of package 200 having protective layer702, in accordance with some embodiments.

As shown in FIG. 8, before packages 110 and 120 are bonded throughbonding structures 215 and 215′, protective layer 702 is formed overpackage 120. Protective layer 702 may be a molding compound. Protectivelayer 702 has a height H_(M), which is smaller than a height H_(c) ofconductive pillar 214 a or a height H_(p) of conductive pillar 214 d.Protective layer 702 covers solder 212 and a portion of conductivepillar 214 a and a portion of conductive pillar 214 d. Even if thesecond reflow process is performed, solder 212 which melts, conductivepillar 214, and conductive pillar 214 can be held by protective layer702. Therefore, conductive pillar 214 a and conductive pillar 214 d areprevented from collapsing. The yield of package structure 200 issignificantly increased.

In some other embodiments, the melting point T₁ of solder 212 is higherthan the melting point T₂ of solder bump 221 (or that of solder 222).Therefore, protective layer 702 may not be needed since solder 212 maynot melt during the second reflow process. In some embodiments, themelting point T₁ in a range from about 200□ to about 220□, and themelting points T₂ is in a range from about 220□ to about 270□. In someembodiments, the melting point T₁ is higher than the melting point T₂ bya temperature difference ΔT. The temperature difference ΔT may be in arange from about 20□ to about 50□.

In some embodiments, conductive pillars 214, such as conductive pillar214 c shown in FIG. 6B, is wider than contact pad 206. In these cases,protective layer 702 may not be needed. In some other embodiments,bottom portion of conductive pillars 214, such as conductive pillar 214e shown in FIG. 6D, is wider than contact pad 206. In these cases,protective layer 702 may not be needed.

In some embodiments, height H_(c) of conductive pillar 214 is smallerthan width W_(c) of conductive pillar 214. In these cases, protectivelayer 702 may not be needed. In some embodiments, height H_(p) ofconductive pillar 214 is smaller than width W_(w) of conductive pillar214. In these cases, protective layer 702 may not be needed.

As described above, conductive pillars 214, such as conductive pillars214 a, 214 b, 214 c, 214 d, and 214 e, are attached to contact pads 206of package 120 by solder 212. Therefore, conductive pillars 214 aredirectly disposed on solder 212 (instead of being formed on contact pads206 by plating) and are not in direct contact with contact pads 206.Therefore, the manufacturing process is simple and low-cost. Inaddition, since conductive pillars 214 are tall and slender, pitch Pbetween bonding structures 215 is greatly reduced. Sliding and shifting,which usually occurs in a ball-to-ball bonding process, are prevented.Therefore, the yield of the package is greatly improved.

Embodiments of mechanisms for forming a bonding structure(s) between diepackages are provided. The bonding structures with conductive pillarsenable the reduction of the pitch between the bonding structures. Inaddition, manufacturing process of the bonding structures is relativelylow-cost. Various embodiments of the conductive pillars are alsodescribed.

In accordance with some embodiments, a package is provided. The packageincludes a substrate and a contact pad formed on the substrate. Thepackage also includes a conductive pillar bonded to the contact padthrough solder formed between the conductive pillar and the contact pad.The solder is in direct contact with the conductive pillar.

In accordance with some embodiments, a package structure is provided.The package structure includes a substrate and a second substrate bondedto the substrate through a bonding structure. The bonding structureincludes a first contact pad formed on the substrate and a secondcontact pad formed on the second substrate. The bonding structure alsoincludes a conductive pillar bonded to the first contact pad and thesecond contact pad through a solder element. The solder element is indirect contact with the conductive pillar.

In accordance with some embodiments, a method for forming a packagestructure is provided. The method includes providing a substrate havingcontact pads formed on the substrate and applying solder on the contactpads. The method also includes attaching conductive pillars on thecontact pads by solder between the conductive pads and the conductivepillars. The method also includes providing a second substrate withsolder bumps. The method further includes bonding the solder bumps andthe conductive pillars to form bonding structures between the substrateand the second substrate.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture,composition of matter, means, methods, and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method for forming a package structure, themethod comprising: providing a first substrate having a plurality ofcontact pads formed thereon; applying a first solder on the plurality ofcontact pads; providing a support substrate having a plurality ofcavities; disposing a plurality of first conductive pillars inrespective ones of the plurality of cavities; disposing a plurality ofsecond conductive pillars in respective ones of the plurality ofcavities, wherein a shape of the plurality of first conductive pillarsis different than a shape of the plurality of second conductive pillars;attaching the plurality of first conductive pillars and the plurality ofsecond conductive pillars to the plurality of contact pads by the firstsolder using a first reflow process, the first solder extending betweenthe plurality of contact pads and corresponding ones of the plurality offirst conductive pillars and the plurality of second conductive pillars;after attaching the plurality of first conductive pillars and theplurality of second conductive pillars, forming a protective layer alongsidewalls of the plurality of first conductive pillars and the pluralityof second conductive pillars; and after attaching the plurality of firstconductive pillars, bonding a second substrate to the plurality of firstconductive pillars and the plurality of second conductive pillars with asecond solder, wherein the second solder extends along sidewalls of theplurality of first conductive pillars and the plurality of secondconductive pillars, wherein the second solder directly contacts theprotective layer adjacent a first pillar of the plurality of firstconductive pillars, wherein after bonding the second substrate the firstsolder completely separates the plurality of first conductive pillarsfrom the plurality of contact pads and the second solder completelyseparates the plurality of first conductive pillars from contact pads ofthe second substrate.
 2. The method of claim 1, wherein disposing theplurality of first conductive pillars comprises: disposing the pluralityof first conductive pillars over a surface of the support substrate; andvibrating the support substrate such that the plurality of firstconductive pillars fall into the plurality of cavities.
 3. The method ofclaim 1, wherein the first solder extends through an insulating layer.4. The method of claim 3, wherein the plurality of first conductivepillars has a width less than a width of the first solder extendingthrough the insulating layer.
 5. The method of claim 1, wherein theplurality of first conductive pillars has a non-uniform width.
 6. Themethod of claim 1, wherein after bonding the second substrate, the firstsolder does not contact the second solder.
 7. The method of claim 1,wherein the first solder has a higher reflow temperature than the secondsolder.
 8. The method of claim 1, wherein the second solder does notdirectly contact the protective layer adjacent a second pillar of theplurality of second conductive pillars.
 9. The method of claim 1,wherein at least one of the cross-sectional shape of the plurality offirst conductive pillars and the cross-sectional shape of the pluralityof second conductive pillars is “T” shaped.
 10. The method of claim 9,wherein at least one of the cross-sectional shape of the plurality offirst conductive pillars and the cross-sectional shape of the pluralityof second conductive pillars is rectangular.
 11. A method for forming apackage structure, the method comprising: applying a first conductivematerial to a first contact pad and applying a second conductivematerial to a second contact pad of a first substrate; after applyingthe first conductive material to the first contact pad and the secondconductive material to the second contact pad, attaching a firstconductive pillar to the first conductive material on the first contactpad and attaching a second conductive pillar to the second conductivematerial on the second contact pad; after attaching the first conductivepillar and the second conductive pillar, forming a protective layer overthe first substrate, the protective layer completely covering the firstconductive material and the second conductive material; and attaching asecond substrate to the first conductive pillar and the secondconductive pillar, the second substrate having a third contact pad and athird conductive material on the third contact pad and having a fourthcontact pad and a fourth conductive material on the fourth contact pad,wherein after attaching the second substrate the first conductivematerial completely separates the first conductive pillar from the firstcontact pad, the second conductive material completely separates thesecond conductive pillar from the second contact pad, the thirdconductive material completely separates the first conductive pillarfrom the third contact pad, and the fourth conductive materialcompletely separates the second conductive pillar from the fourthcontact pad, wherein after attaching the second substrate, at least aportion of sidewalls of the second conductive material are free of theprotective layer, the third conductive material extends along sidewallsof the first conductive pillar, and the fourth conductive materialextends along sidewalls of the second conductive pillar, the thirdconductive material directly contacts the protective layer, and thefourth conductive material does not directly contact the protectivelayer.
 12. The method of claim 11, wherein the first contact pad ispartially covered with a first insulating layer, the first conductivematerial extending through the first insulating layer to the firstcontact pad.
 13. The method of claim 11, wherein the protective layercontacts sidewalls of the first conductive pillar.
 14. The method ofclaim 11, wherein the first conductive material has a higher reflowtemperature than the third conductive material.
 15. The method of claim11, wherein the second conductive pillar has a different shape than thefirst conductive pillar.
 16. A method for forming a package structure,comprising: applying a first conductive material to a first contact padof a first substrate; after applying the first conductive material tothe first contact pad, reflowing the first conductive material andattaching a first end of a first conductive pillar to the firstconductive material; after reflowing the first conductive material,forming a protective layer on the first substrate, the first conductivepillar protruding through the protective layer; and after forming theprotective layer, reflowing a second conductive material attaching asecond end of the first conductive pillar to a second contact pad of asecond substrate, thereby bonding the first substrate to the secondsubstrate, wherein after reflowing the second conductive material thefirst conductive pillar is spaced apart from the first contact pad andthe second contact pad, wherein the second conductive material contactssidewalls of the first conductive pillar, wherein the first conductivematerial has a higher reflow temperature than the second conductivematerial, wherein the second conductive material directly contacts theprotective layer; and attaching the first substrate to the secondsubstrate using a second conductive pillar, wherein attaching the firstsubstrate to the second substrate using the second conductive pillarcomprises: attaching the second conductive pillar to a third contact padon the first substrate with a third conductive material; and attachingthe second conductive pillar to a fourth contact pad on the secondsubstrate with a fourth conductive material, wherein the fourthconductive material extends along sidewalls of the second conductivepillar, the fourth conductive material being spaced apart from theprotective layer.
 17. The method of claim 16, wherein the protectivelayer completely covers the first conductive material.
 18. The method ofclaim 16, wherein the protective layer is formed on an insulating layer,wherein the first conductive material contacts the insulating layer. 19.The method of claim 16, wherein the first conductive pillar has adifferent shape than the second conductive pillar.